1. Field of the Invention
The present invention relates to a geomagnetic sensor for azimuth detection and a method thereof. More particularly, the present invention relates to a geomagnetic sensor for accurate azimuth detection, which compensates for the influences of inclination before calculation of magnetic dip, and a method thereof.
2. Description of the Related Art
A geomagnetic sensor operates to measure intensity and direction of a terrestrial magnetism which a human can not perceive, and in particular, a sensor which operates to measure the geomagnetism using a fluxgate is called a fluxgate type geomagnetic sensor.
The fluxgate type geomagnetic sensor includes a fluxgate core made of a material having a high magnetic permeability such as permalloy, or other such material known in the art, a driving coil wounding the core, and a detection coil. Two or three fluxgate cores may be employed. The fluxgate cores are built in perpendicular relation with each other. Accordingly, a two-axis fluxgate sensor is formed of X and Y-axis fluxgates, while a three-axis fluxgate sensor includes X, Y and Z-axis fluxgates. As a driving signal is received at each driving coil wound on the fluxgate cores, magnetism is transduced by the cores. Therefore, by detecting a secondary harmonic component in proportion to an external magnetic field using the detection coil, the magnitude and direction of the external magnetic field can be measured.
The magnetic field has a certain orientation, and therefore, measurement varies depending on the postures of the geomagnetic sensor. In other words, discrepancy may occur between a measured azimuth and an actual azimuth when the geomagnetic sensor is in inclined posture during sensing. In order to eliminate such a problem, the recent suggestion was that a tilt angle is measured using a proper sensor such as an acceleration sensor, so that the measured tilt angle can be used to compensate for the influence by the inclination of the geomagnetic sensor and subsequently provide an accurate azimuth angle. A geomagnetic sensor using a three-axis fluxgate does not necessarily take a dip angle λ into account. However, the dip angle needs be considered especially when the geomagnetic sensor uses a two-axis fluxgate. Because in the case of a two-axis fluxgate sensor, there are only X and Y-axis fluxgates placed on the earth's surface, an azimuth is measured using only the horizontal component value of an actual geomagnetic vector incident on the earth. In other words, the ‘dip angle’ refers to an angle by which the terrestrial magnetism enters the earth's surface, and therefore, cos λ needs be multiplied by the vector of the actual terrestrial magnetism which is measured by the fluxgates. For this reason, the two-axis fluxgate sensor requires information about dip angle.
Conventionally, a two-axis fluxgate sensor either estimates a dip angle or receives information about dip angle from an external device such as a global positioning system (GPS), or other such system known in the art. However, the estimated dip angle received in this way is often not accurate, and therefore, causes a problem that the azimuth angle information may be distorted. Using the external device such as GPS to receive information about dip angle also requires additional equipment for communication with the external device. Thus, the size and manufacturing cost of the geomagnetic sensor increases. Meanwhile, there has been an attempt to compute the dip angle within the geomagnetic sensor. However, it is difficult to obtain an accurate dip angle by computation, and the geomagnetic sensor is burdened with increased computations to obtain the dip angle.
Even though it does not require dip angle, the three-axis fluxgate sensor also has a problem. That is, because a Z-axis fluxgate is additionally required for the three-axis fluxgate sensor, the size of the sensor inevitably increases, and therefore, the sensor is somewhat inappropriate for use in a portable electronic appliances.